I'm still a Beginner in Magento and I was given a task to upload/create 600 Categories and have a hierarchy up to 4th subcategory. I've been searching for a while now, and most return paid extensions. Would someone be kind enough to help me perform this or point me to a guide? So far I have found a random script; it ran well with no errors yet still didn't create any category.

Here is a nice extension (look for "Import/Export Magento Category Extension" in the page) that can import/export a tree of categories.
You have to build a csv file with your categories in a specific format (nothing fancy though) and place it in a folder of your magento instance, then run some actions in the admin.
I don't really like the fact that the source file must be placed on the disk , but with some small changes it can be changed to accept a file upload.